ph-responsive glass electrodes



Patented Feb. 14, 1950 UNITED STATES PATENT OFFICE pH-RESPONSIVE GLASS ELECTRODES No Drawing. Application December 12, 1947,

Serial No. 791,461

My invention relates to pH-responsive glass electrodes, utilizable for example in determination of magnitudes of pH,, representative of, the magnitudes of concentrations of hydrogen-ions or hydroxyl-ions or, more simply, for determination of the degrees of acidity or alkalinity of solutions; more particularly my invention in concerned with electrode glasses, of new compositions exhibiting characteristics hereinafter referred to, from which may be blown or otherwise formed the significant pH-responsive glass membranes of electrode structures.

The more significant qualities of my herein described and claimed pH-responsive electrodes of glass are:

Electrical volume-resistances of significantly new low orders of magnitude, rendering the measuring of pH substantially free of interfering external electrical effects andpermitting use of simpler or less sensitive measuring instruments; sodium errors, after prolonged continuous use of my electrode in test solutions at ordinary or high temperatures (e. g. near 90 C.) as low as, or even lower than, those of heretofore known glass electrodes; and a voltage/pH characteristic which is reproducible and rectilinear, like that of the hydrogen electrode, from pH to 14 pH in event of absence from the test solution of ions of sodium, potassium, or lithium, and in event of presence of such ions it is rectilinear and reproducible from 0 6 Claims. (Cl. 204195) 2 pH to about 9 pH and from there on to 14 pH is reproducible. The slope of the rectilinear characteristic at 25 C. is defined by the fact a change of about 59.1 millivolt corresponds with 1 pH, therefore following the Nernst equation.

Further in accordance with my invention it is characteristic of my glasses that they are broad 1y fundamentally of the lithia-silica class, with inclusion of one or more of the oxides CSaO, RbzO, K20, NazO and those herein contemplated oxides having the effect of increasing the ratio of oxygen to silicon in the glass'network; the one or more oxides aforesaid in combination with the lithia silica mixture per se imparts or improves workablity, besides improving it in one or more of i the aspects of low sodium error, low electrical volume-resistance, operating stability and reprotrodes of glasses having the characteristics here inafter described.

For an understanding of my invention reference may be had to Table 1 below, which includes examples of my preferred and additional glasses comprehended by my invention.

Table I Composition in M01 Percent pH Error at 25C.; 2 Normal Na, 12.8

. pH Res. at No. 2 Q,

Megs. Days Months L190 C830 Rbzo K10 N810 L520: S10:

' v 5 i e WWWWNONNNNNQOOQOONWNN OOQOOOOOGOWOSOOOOQOOCOO It is a broad aspect of my invention that in addition to silica and lithia there shall be used one or more constituents of the broad group consisting of the two sub-groups which are, respectively, the oxides later referred to and including La2O3 and the oxides of the alkali metals Cs2O, Rb20, K20 and Na2O, so that, broadly expressed, my invention is exemplified by the mixture of the formula:

(1) SiO2-Li2O-one or more oxides of the group consisting of the oxides. T102, MnO2, MnzOa and the rare earth metal oxides including La2O3 and PrzOs, and C520, R1020, K20, NazO.

In general, and broadly, the qualitative aspects of my invention, as represented by the prefusion compositions of my glasses, are shown by the foregoing and following. formulae:

(2), Li20-Cs2O (and/or Rb2O)-Si02; or

( 3) Li2O-SiO2La2O3 (generically representing one or more of the oxides consisting of Ti02, MnOz, MnzOa and the rare earth metal oxides including LasOs and PrzOa) or (4) LizO-one or more of Cs2O, Rb20, K20,

Na2O-SiO2La2O3 (generically representing one or more of the oxides consisting of T102, M1102, M11203 and the rare earth metal oxides including La2O3 and P1203).

' For procuring or increasing workability of the fundamental Li2OSiO2 (lithia-silica glass) mixture, there may be included in the mixtures of foregoing Formula 4 either or both of the oxides K20 and NazO preferably in proportion or proportionsnot materially affecting one or both of the characteristics low electrical volume-resistance and low sodium error.

None of foregoing four formulae, broadly definitive of my invention, includes an oxide of any of the alkaline earth metals one or more of which heretofore commonly has constituted a component of pH-responsive glasses.

Li2O of the foregoing formulae is important as conducive to or for attaining suitably low electrical Volume-resistance and is eiiectively usable herein for such purpose and, in general, it is of import in the matter of reduction of sodium error in event the test solution'contains sodium-- ions.

Within the limits set forth in Table I, SiOz, the other component of the fundamental Li20- SiO mixture of my glasses, while in general favorable to imparting or contributing to the glass low electrical volume-resistance, is conducive to high sodium error. However SiO2 with Li2O together constitute the fundamental and greatest component of my prefusion mixtures, and they together impart to or procure for my glasses low electrical volume-resistance and low or at least moderate sodium error.

In the foregoing Formulae 2 and 4, Cs2O and/or Rb20 has the effect of imparting operating chemical stability or durability to the glass and is of importance in procuring or contributing to procuring low sodium error; which characteristics obtain also with respect to the oxides herein contemplated and examples of which appear below; furthermore, any one or more of C520, Rbz O, KzO-aild N220 renders the SiOa- Li2O mixture workable for imparting thereto sufficient ruggedness and rigidity for practical purposes and for safely withstanding the necessary handling thereof incident toiits use; and similarly the oxides of the group including LazOs, of

Formulae 3 and 4, have the same or similar effects. The C820, Rb20, K20, Na2O and the oxides of the group including La203 are to useful degree interchangeable, as indicated by Formulae 2 and 3 in which the Cs2O and/orequivalent component and the oxides of the other group (including LazOs) are in general substitutable for each other, and also usable in conjunction with each other (Formula 4). Table I shows that a glass made up from a prefusion mixture of SiOz, Li2O, La20a with either Na2O or K20, requires the presence of C520 and/or RbzO if a low sodium error is to be obtained. Thus CszO and/or La2O3 are essential for the production of low sodium error glasses.

In Formulae 3 and 4 La2O2 may constitute the oxide component employed, and in an event it generically represents any one or more of the oxides having any one or more of the effects of procuring or assisting to procurewcrkability of the glass, reducing electrical volume-resistance, reducing sodium error, and increasing operating stability of the glass. One or more or the oxides used may be chosen from the group P205, TiOz, T603, 2102, CbzOs, T3205, T1102, B203, MnOz, M11203, the rare earth metal oxides La2O3, P1203, NdzOs, 0e02, and the oxides of the further rare earth metals yttrium, Yt; Samarium, Sm; europium, Eu; gadolinium, Gd; terbium, Tb; dysprosium, Dy; holmium, Ho; erbium, Er; thulium, Tm; ytterbium, Yb; and lutecium, Lu.

Referring to Table I all or the prefusion glass compositions include Li2O in mol per cent ranging from 26 to 30, and S102 ranging from 63 to' 69. All oi the prefusion glass compositions except No, P include at least 'one added alkali metal selected from the group consisting of CszO, R1020, K20 and Na2O. Prefusion composition P includes 5 mol per cent of LazOs. All prefusion compositions in Table I except No; V include an oxide selected from the group consisting of T102, MnOz, Mn2O3 and the rare earth metal oxides La2O3 and PrzOs. No. V includes Cs2O,'3 mold per cent, a high percentage of silica, 69 mol per cent, and lithia, 28 mol per cent. Thus, the glass of prefusion composition V illustrates the lowered electrical volume resistance resulting from the relatively high mol percentages of lithia and silica with a sodium error which, though higherthan the characteristics of other glasses from Table I, may be considered a moderate sodium error as compared with prior art glasses. No. P with its relatively high mol percentages of lithia and silica and the high mol percentage of La2O3 is illustrative of another composition for a glass of low volume electrical resistance with moderate sodium error, and with No. V forms the basis of the statement of limited interchangeability between the two sub-groups.

In Table I are found numerous compositions qualitatively and quantitatively exempliying my invention in the broad sense they are respectively comprehended by qualitative Formulae 1, 2, 3

' and 4 hereinbefore appearing, and quantitatively impairedl Indicated sodium errors in terms of pH as appearing in Table I were measured under conditions of "2N sodium solution of 12.8 pH, at 25 C. It will be observed that all of the glasses of Table I have compositions represented by three-component prefusion mixtures in which the first component consists of about 69 mol per cent to about 63 mol per cent silica, a second component consisting of about 26 mol per cent to about 30 mol per cent lithia, and a third component consisting essentially of at least one oxide from the group Ti02, Mn02, Mn203 and the rare earth metal oxides including La203 and PrzOs, and/ or of at least one additional alkali metal oxide from the group Cs20, Rb20, K20 and Na20, the sum of the mol per cent of the first oxide group and the mol per cent of the added alkali metal oxide group being not less than about 3 nor more than "about 10, the permissible mol per cent of the first oxide group ranging from to about with the permissible moi per cent of the added alkali metal oxide group in any case ranging from 0 to about 5. For composition No. P there is 0 mol per cent of any additional alkali metal oxide, while with composition No. V there is 0 per cent of the oxides of the first-named group. However, when the mol per cent of the oxides including LaOsis less than 3, the balance of said sum is made up of Cs2O. It is to be further observed, prefusion glass mixtures Nos. M and N, that where Na is present in the mixture, there is also included a greater mol per cent of the alkali metal oxide Cs20 than the mol per cent of Na20. For the foregoing conditions Rb20 may replace Cs20. It will be further observed, prefusion glass mixture No. 0, that where there is present in the mixture K20, a mol per cent of the alkali metal oxide Cs20 of not less than about two-thirds that of the K20 is included. Again, Rb20 may be substituted for Cs20. The foregoing characteristics are common to the prefusion glass mixtures A-F and K-V.

Where low sodium error is of lesser importance than low electrical resistance, there may be used such compositions as exemplified by glasses A-H, 0-8, and V. In the foregoing glasses it will be observed that the sum of the mol per cent of the oxide group including La203 and the mol per cent from the added alkali metal oxide group is not less than about 3 nor more than about 9. It is to be further observed that when the mol per cent of oxides including La2O3 is less than 3 (preiusion glass mixtures A, Q and V), the additional alkali metal oxide Cs20 is selected for the balance of said'sum, and Where the mol per cent of the oxide from the group including La202 is more thanabout 3 and there is to be a selection of two additional alkali metals, that selection shall be limited to Cs20 and K20 (prefusion glass mixture 0).

And for examples of my glasses or compositions having both low sodium error and low electrical resistance, reference may be had to such glasses as B, C, D, E, F, K, 0, and R. The foregoing glasses are four-component glasses, which have low sodium error, less than 1.0 pH after six months, and have electrical volume-resistances from 5 to 105 megohms. GlassesB, C, D, E, F, 0 and B have resistances from 5 to 85 megohms. It will be observed that for these compositions the sum of the mol per cent of the oxide of the group including La202 and the mol per cent of the added alkali metal oxide is not less than about -6 nor more than, about 9. It will be fure therobserved as. pointed out inoconnection with prefusion glass mixture 0, that when there is present K20, then there is also present the alkali metal Cs20 in amount not less than about twothirds the mol per cent of the K20. Rb20 may also be selected in place of Cs20.

' For examples of my glasses or compositions having low sodium error (which at 25 C., 2 nor-.

-mal Na, is less than 1.0 pH, both after five days and after six months), reference may be had to such glasses as B-F, K-O, R and U. It will be observed' that eachglass is of the four-compo-e nent type where the sum of the mol per cent of the oxide group including La203 and the mol per cent of the added alkali metal oxide group is not less than about 6 and not more than about 10. As already explained, in the foregoing prefusion mixtures,-where the alkali metal oxide K20 is present, there is also present at least one of the alkali metal oxides Cs2O and Rb20 in amount not less than about two-thirds of the mol per cent of K20. For each mixture including the alkali metal oxide Na20, there is also present the alkali metal oxide Cs2O in amount about one and one-half times the mol per cent of the Na20. In the foregoing, Rb20 may be substituted for C520.

It is to be further observed that prefusion compositions B, C and D consist of four components as follows: silica 64-67 mol per cent, lithia 27-28 mol per cent, 3 mol per cent Cs2O, and from 3-5 mol per cent La2O3, yielding glasses having relatively low volume electrical resistance and low sodium error.

The more specific, quantitative, aspect of my invention to which it is not limited i. e. suitable proportions (herein expressed in mol percentages) of the constituents of the prefusion mixtures for my g1asses,-is exemplified by the following formulae:

(5) From about 26% to about 30% Li20-from about 0% to about 5% of one or more Cs20, Rb20, K20, Na20-from about 63% to about 70% -SiO2;

(6) From about 26% to about 30% Li20--from about 63% to about 70% Si02-from about 0% to about 5% La202 (generically reprefsenting one or more of the oxide group which includes La20a or v (7) From about 26% to about 30% Li20-from about 0% to about 5% of one or more Cs20, Rb2'0, K20, Na20-from about 63% to about 70% SiOz-from about 0% to about 5% LazOs (generically representing one or more of the oxides which, include LazOg, PlzOs, T102, MI102 and M11203.

It shall be understood that the aforesaid mol percentages, or ranges thereof,.are not critical; it shall be understood that on these quantitative aspects of my invention that the use of percentages of one or more of the constituents of any particular mixture prooures or assists in procuring one or more of the characteristics of my glasses, because even smaller proportions than those indicated and/or higher than those indicated are utilizable without departure from-the broad aspects of my invention.

, With respect to Formulae 5, 6 and '7 it shall be understood that for purposes of procuring or increasing workability of the fundamental, dom inant, lithia-silica component per se, there may be included in my compositions as above described with respect to Formulae 1, 2, 3 and 4 either of the oxides K20 and Na2O preferably in amountswhich will maintain at approximately the' 'orlginal magnitude the total of the percentages "of the respective components; which connotes that by such addition of either of K20 and Nazo there is permissible a decrease in percentage of one or more of the constituents SiOz, L120, CszO (and/or R1320), LazOs (generically representing one or more of the oxides LazOs, PrzOa, T102, M1102 and MnzOa) l Of the glasses included in Table I, my preferred ones are those lettered B, C, D, E, F, K, L, M, N, O, Q, R, S, U; in glass Q of Table I the total of C520 and LazOs components is about 4 mol per cent.

Aforesaid characteristically low electrical resistance of my glasses is of decided practical advantage because there may be used therewith, for example, a measuring system of potentiometer ype with a galvanometer which has a current sensitivity of the order of 5x10- ampere per millimeter of scale at a distance of 1 meter from the reflector of the galvanometer. In any event, the current passing through my low resistance electrode glasses is many times greater in magnitude than the magnitude of the necessarily extremely minute current passing through the high resistance electrode glasses heretofore commonly employed; for example, the magnitude of the current passing through my low resistance glasses is of the order of 100.0r more times that obtaining with the high resistance glasses of aforesaid prior practice. Accordingly my glasses of low resistance connote the practicability of use therewith of measuring means which are relatively simple and less costly than those required for high resistance glasses. With my glasses of low volume-resistance there is not required to be used therewith either a measuring system of high impedance such, for example, as that of Patent 2,108,294, or as an alternative thereto an instrument such as a Compton type of quadrant electrometer. Measuring systems of the general type of that of aforesaid Patent 2,108,294, or the like, are of high impedance, because the impedance or resistance of the glass electrodes for which they are adapted is high, and therefore necessarily must deal with extremely minute currents passing through the electrode glasses whose resistance heretofore has been of significantly higher order than about 100 megohms.

The low resistance of my glasses is of further significant advantage because they render less significant or overcome those difficulties, encountered in industrial measurements of pH by glass electrodes of aforesaid high resistance heretofore commonly used, caused by external electrostatic fields which necessitate careful shielding of the apparatus or significant parts thereof, as exemplified by Patent 2,256,733; and/or caused by leakage currents, particularly when the apparatus is used under conditions of humidity of the ambient atmosphere, the, leakage currents in some cases being more troublesome even than external electrostatic fields aforesaid.

The prefusion mixtures of oxides for my glasses are readily fusible at temperatures from about 1600" F. to about 2200 R, and the rate of fusion is greater, more rapid, than in the case where one-or more oxides of the alkaline earth metals are present in the prefusion mixture; and temperatures from about 800 F. to about 1100 F. serve for working, including blowing, of my glasses. Furthermore my glasses, besides having aforesaid significant lower electrical resistances than those :having asxheretofore acomponent of one or more of the oxides of the alkaline earth metals (such as Ca, Sr, Ba, Mg) the pH-response of my glasses is excellent; their sodium error is low and their stability or durability when continuously used over relatively long periods in contact with test solutions, containing sodium-ions and ranging in temperature from 25 C. to more than 6., is high; and their pH errors at 25 C., in 2 normal sodium of 12.8 pH, after continuous use for as long as six months, are low and range to as low as 0.09 pH, as indicated in aforesaid Table I; and for a membrane whose dimensional characteristics may be those of the example stated in my Patent No. 2,444,845, column 10, lines 48-50, namely, for bulbs of approximately 8 mm. to 9 mm. outside diameter, a weight of about .15 gram, joined to a stem of approximately 10 mm. internal diameter, and having membrane thickness of about .2 mm, aforesaid low electrical volumeresistances range from about megohms at 25 C. to as low as 5 megohms or lower, and at temperatures of the test solutions up to about 90 C. said resistances at test solution temperatures diminish to small fractions, sometimes as low as'a few thousandths of their magnitudes at 25 C. The volume-resistances of Table I were obtained in each case by measurement of resistances between conductors in solutions respectively disposed on opposite sides of and engaging all of the membrane of the glass electrode. The resistances of the membranes at 90 C. are approximately five-'thousandths of the resistances at 25 C., the latter being the temperature at which the measurements were made for Table I.

It is an important aspect of my invention that the compositions of my glasses which have one or more of the characteristics aforesaid are represented by prefusion oxide mixtures which do not contain nor require any one or more of the oxides of the alkaline earth metals which, if present would, in some instances, contribute no improvement in any of the aforesaid characteristics but in some cases would be of disadvantage.

The proportions herein named are in mol per centages.

What I claim is:

' 1. A pH-responsive glass electrode including a conductive membrane of glass Whose composition is represented by a three-component prefusion mixture free of the alkaline earth metals, the first component consisting of about 69 mol per cent to about 63 mol per cent silica, a second component consisting of about 26 mol per cent to about 30 mol per cent lithia, and the balance a third component consisting essentially of at least an oxide selected from a first group consisting of T102, MnOz, M11203 and the rar earth metal oxides including LazOs and PI203, and of at least one added alkali metal oxide selected from a second group consisting of the following: C520, R1020, K20 and NazO, the sum of the mol per cent of at least one of said oxides of said first group and at least one of said alkali metal oxides of said second group being not less than about 3 nor more than about 10, the permissible mol per cent of the oxides from said first group ranging from 2 to about 5, there being present in each mixture including NazO a greater mol per cent of at least one of the alkali metal oxides Cs-2O and R1020 than the mol per cent of NazO, and there being present in each mixture including K20 a mol per cent of at least one of said alkali metal oxides C820 and RbzO of not less than about two-thirds that of the K20, the mol per cent of alkali metal oxide ranging'from 0 to about 5,

2. A pH-responsive glass electrode including an electrically conductive membrane of glass with. a

low electrical volume-resistance of the order of from 5 to 85 me'gohms at 25 C., the composition of said glass membrane being represented by a three-component prefusion mixture free of alkaline earth metals, the first component consisting of about 69 mol per cent to about 64 mol per cent silica, a second component consisting of about 26 mol per cent to about 30 mol per cent lithia, and the balance a third component consisting essentially of the sum of at least one oxide selected from a first group consisting of TiOz and the rare earth metal oxides including LazOs and P1'2O3, and of at least one added alkali metal oxide selected from a second group consisting of the following: C520, RbzO and K20, said sum of thefmol per cent of at least one of the oxides of said first group and of at least one of the added alkali metal,

oxides of said second group being not less than about 3 nor more than about 9, the permissible mol per cent from said first group ranging from 2 to about 5, and the permissible mol per cent from said second group ranging from to about 5, the added alkali metal oxide C520 being selected for the balance of said sum where the mol per cent from said first group is less than about 3, and only C520 and K20 being jointly selected for the balance of said sum where the mol per cent from said first group is more than 3 and when two oxides of said second group are selected.

3. A pH-responsive glass electrode including an electrically conductive membrane of glass characterized by a low sodium error which at 25 C., 2 normal Na, at 12.8 pH, is less than pH 1.0", both after five days and after six months, the

composition of said glass membrane being rep-v resented by a four-component prefusion mixture free of alkaline earth metals, the first component consisting of about 67 mol per cent to about 63 mol per cent silica, a second component consisting of about 26 mol per cent to about 28 mol per cent lithia, a third component consisting essentially of at least one oxide of about 3 mol per cent to about 5 mol per cent selected from a group consisting of MnzOs and the rare earth metal oxides including 119.203 and H203, and the balance a fourth component of about 3 mol per cent to about 5 mol per cent of at least one added alkali metal oxide selected from a second group consisting of the following: 0e20, RbeO', K20 and Nazo, the sum of the mol per cent of the third and fourth components being not less than about 6 and not more than about 10, there being also present in each mixture including the alkali metal oxide K20 a mol per cent of at least one of said alkali metals C820 and RbzO not less than about two-thirds of the mol per cent of K20, and there being also present in each mixture including the alkali metal oxide NazO a mol per cent of at least one of the alkali metal oxides C520 and RbzO about one and one-half times the mol per cent of NazO.

4. A pI-I-responsive electrode of glass whose composition is represented by a prefusion mixture consisting of about 28 mol per cent L120, 64-67 mol per cent S102, about 3 mol per cent C520 and from 3 to 5 mol per cent LaaOs.

5. A pH-responsive electrode of glass whose composition is represented by a prefusion mixture consisting of about 28 mol per cent LizO, about 65 mol per cent S102, about 3 mol per cent CsaO, and about 4 mol per cent PrzOs.

6. A pH-responsive electrode of glass whose composition is represented by a prefusion mixture consisting of about 26 mol per cent LiaO, about 65 mol per cent S102, about 3 mol per cent K20, and a total of about 6 mol per cent 0520 with LaaOa.

GEORGE A. PERLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,233,486 Locke July 17, 1917 2,215,039 Hood et al Sept. 1'7, 1940 2,462,843 Cary et a1 Mar. 1, 1949 OTHER REFERENCES Glass Electrode, by Dole (John Wiley & Sons) 1941, pages 64, 74, 75, 79. 

1. A PH-RESPONSIVE GLASS ELECTRODE INCLUDING A CONDUCTIVE MEMBRANE OF GLASS WHOSE COMPOSITION IS REPRESENTED BY A THREE-COMPONENT PREFUSION MIXTURE FREE OF THE ALKALINE EARTH METALS, THE FIRST COMPONENT CONSISTING OF ABOUT 69 MOL PER CENT TO ABOUT 63 MOL PER CENT SILICA, A SECOND COMPONENT CONSISTING OF ABOUT 26 MOL PER CENT TO ABOUT 30 MOL PER CENT LITHIA, AND THE BALANCE A THIRD COMPONENT CONSISTING ESSENTIALLY OF AT LEAST AN OXIDE SELECTED FROMA FIRST GROUP CONSISTING OF TIO2, MNO2, MN2O3 AND THE RARE EARTH METAL OXIDES INCLUDING LA2O3 AND PR2O3, AND OF AT LEAST ONE ADDED ALKALI METAL OXIDE SELECTED FROM A SECOND GROUP CONSISTING OF THE FOLLOWING: CS2O, RB2O, K2O AND NA2O, THE SUM OF THE MOL PER CENT OF AT LEAST ONE OF SAID OXIDES OF SAID FIRST GROUP AND AT LEAST ONE OF SAID ALKALI METAL OXIDES OF SAID SECOND GROUP BEING NOT LESS THAN ABOUT 3 NOR MORE THAN ABOUT 10, THE PERMISSIBLE MOL PER CENT OF THE OXIDES FROM SAID FIRST GROUP RANGING FROM 2 TO ABOUT 5, THERE BEING PRESENT IN EACH MIXTURE INCLUDING NA2O A GREATER MOL PER CENT OF AT LEAST ONE OF THE ALKALI METAL OXIDES CS20 AND RB2O THAN THE MOL PER CENT OF NA2O, AND THERE BEING PRESENT IN EACH MIXTURE INCLUDING K2O A MOL PER CENT OF AT LEAST OF NOT LESS THAN ABOUT METAL OXIDES CS2O AND RB2O OF NOT LESS THAN ABOUT TWO-THIRDS THAT OF THE K20, THE MOL PER CENT OF ALKALI METAL OXIDE RANGING FROM 0 TO ABOUT
 5. 